An impressive list at first glance, but its credibility really starts to unravel as you look closer at this organization. First of all, how many certified structural engineers are part of this petition? Architects know nothing of structural collapse scenarios (the ring leader admits this), and probably most engineers (unless specialized in mechanical engineering field) wouldn't know much either. Then, even a small few of mechanical engineers would know about how buildings can fall. My father is an electrical engineer and can't fix a door hinge, so if he joined this cause I'd have to seriously question its validity.
One could easily start an organization about Neuro Surgery and get numerous Phds and MDs to sign a petition on the matter, but one would have to really examine the list of members and see what their disciplines are before placing any credibility in their collective views no? This is not to say they aren't intelligent people, but are they qualified to speak on the subject to such an extent as to suggest such collaborative corruption by so many different people and agencies? Moreover, how do we know without question that some of these people are who they claim? In two cases, one was lieing about his identity and one was a made up name. As for the rest, one can only speculate and also accept that even intelligent people can be fooled and used.
Here's an independent take I hope you will find interesting.